The work will comprise clinical research in nutrition to enlarge understanding of the metabolism of micronutrients, particularly of the mechanisms whereby vitamin B12 and folate are absorbed, transported, distributed, stored excreted, and the ways in which they participate in metabolic reactions and interactions. The broader aim is understanding physiologic and biochemical concepts generally applicable in the field of human nutrition. A major focus is development concepts generally applicable in the field of human nutrition. A major focus is development of new methodology and techniques, including improved assays for biologically important substances (e.g., vitamin B12 and folate binders), aimed at providing more accurate tools for diagnosis and differentiation of nutritional derangements. A major objective is further delineation of total daily requirements for vitamine B12, folate, and other nutrients, factors which affect their availability and absorption, and the detection and significance of selective nutrient deficiency affecting only some cell lines. Finally, substances promoted as nutritional or dietary supplements without prior adequate monitoring will be monitored for safety of human use.